Regulator controlled by electron tube



June 27, 1950 s. A. HOLMQVIST 2,513,024

REGULATOR CONTROLLED BY ELECTRON TUBE Filed Nov. 24, 1947 Fig. 2

Patented June 27, 1950 REGULATOR CONTROLLED BY ELECTRON TUBE Seth August Holmqvist, Appelviken, Sweden, as-

signor to Telefonaktiebolaget L. M. Ericsson, Stockholm, Sweden, a company of Sweden Application November 24, 1947, Serial No. 787,767 In Sweden December 3, 1946 4 Claims. 1

It is important to incorporate safety devices in all apparatus controlled by regulators, in order to protect the apparatus in case any of the parts thereof should become inoperative. As an example We can mention a regulator for keeping the temperature in an oven constant. The temperature-sensitive member, i. e. the transmitter in such a regulator, is always subjected to great stresses, and when some defect occurs in said member, the heating element of the oven should be turned off to prevent the temperature from damaging the oven or its contents. In electron tube controlled regulators, such safety devices are known, in which the heating element of the oven is automatically turned off upon the occurrence of certain defects in the temperature sensitive member, e. g. open circuiting thereof. Said devices have the disadvantage, that the heating element of the oven is not turned off on the occurrence of a short-circuit in the temperature-sensitive member. The present invention has for an object the elimination of such disadvantage and to provide a safety device for use with electron tube controlled regulators, which device is operative for short-circuits in the transmitter as well as for other defects.

The invention will be described more in detail with reference to the accompanying drawing, in which Fig. l is a circuit diagram showing the principle for a known form of simple vacuum tube regulator for keeping the temperature in an oven constant, and Fig. 2 is a similar diagram of a regulator of the same type designed according to the invention.

The two circuits shown in Figs. 1 and 2 operate according to the following fundamental principle. The heating element E of the oven u is turned on by a relay A having a contact K. Relay A is disposed in the anode circuit of an amplifying tube II. The anode current in said tube and therefore relay A is controlled from a temperature-sensing transmitter R6 disposed in the oven and having the form of a resistance, in connection with an amplifying tube I. When the anode current in the amplifying tube II increases to a certain value, the heating element E is turned on by relay A, and when the anode current decreases below a certain value, the current supply to the heating element E is turned off by said relay.

To begin with, the known circuit shown in Fig. 1 will now be described in detail. From the secondary winding S3 of a transformer T, the primary winding P of which is supposed to be connected to a source of alternating current, current is supplied to a bridge circuit comprising a fixed resistance R5, a potentiometer R4 and the temperature-sensitive resistance R6 arranged in the oven u. The oven is heated by means of the heating element E. c is a sliding contact which is adjustable along the potentiometer R4. The voltage fed to the grid of the tube I, which voltage is obtained from the sliding contact 0, is determined by the position of said contact and by the relation between the resistances R5 and R6. The anode voltage for the tube I, which is provided with an anode resistance RI, is supplied from the winding SI on the transformer T, which voltage is rectified by the rectifier L and the voltage thus obtained is filtered in a way known per se by means of a filtering circuit containing the condensers CI and C2, the resistance R2 and the lead LI. The anode circuit of the amplifying tube 11 is fed from the winding SI through the relay-winding A. The alternating current am- :plified by the tube I is supplied to the grid of the tube II through the coupling condenser C3. Said grid is also fed from the secondary winding S2 of the transformer T through the grid resistance R3, with a voltage which is chosen so that the anode current in the tube II is so low that the armature of the relay A is released when no voltage has been supplied to the grid of the tube II from tube I over the condenser C3. Since the anode circuit of the tube II is fed with current from the secondary winding S I, the anode current in the tube will be dependent on the phase relation between the voltages on the grid and the anode of the tube II. During those half cycles in the alternating current when the anode is negative (relatively to the cathode) the anode current is always zero. During the positive half cycles, the magnitude of the current is dependent upon the grid voltage. If this latter is positive (the same phase position) anode current will appear, and if it is negative, the anode current will remain zero also during said positive half cycle.

If the resistance values in resistances R5 and R6 are equal and contact 0 occupies a position in the middle of the resistance R4 (a=b), the voltage feeding the grid of the tube I is zero, and the grid voltage on tube II is thereby determined only by the voltage of the secondary winding S2. The anode current in the tube II is thus zero, and relay A is released. If the temperature in the oven now decreases, the resistance value of resistance R6 decreases, the balance of the bridge circuit is disturbed and an alternating voltage is supplied to the grid of tube I. Said voltage is amplified and fed to the grid of tube II. The

thereby increasing and the balance in the bridge circuit being re-established, whereby the grid voltage on tube I becomes zero and relay A again turns off the heating element E. Shouldthe temperature increase above the value to which the temperature has been set beforehand, the

resistance of the transmitter RB will increase and the balance in the bridge circuit will be disturbed again, the grid in tube I then being fed with a voltage which is 180 out of phase relatively to the voltage which is fed thereto when the temperature is too low in the oven. This entails that the grid in tube II is fed with a voltage which is 180 out of phase relatively to the anode voltage, due to which the anode current will remain zero even during the positive half cycles of voltage applied to the anode in tube II. The armature of the relay A therefore remains released'and the heating element E is not turned on. The desired temperature in the oven can be set beforehand to a suitable value by adjusting the contact on the potentiometer R4.

A greatfadvantage with the above described prior art regulator is that if some of the delicate parts should become inoperative, the heating element of the oven is turned ofi. This is true for instance as regards both the electron tubes, the rectifier L and the transformer T. The most delicate part of the regulator is however the transmitter R6, An open circuit condition in said transmitter corresponds to an infinitely high temperature in the oven, due to which relay A turns off the oven heating element E. A shortcircuit in the transmitter R6 or in its connecting leads, onthe other hand, corresponds to a low oven temperature, due to which relay A remains energized and the oven element E remains turned on, independent of the temperature of the oven.

This disadvantage is eliminatedby means of the arrangement shown in Fig. 2, in which, ac-

cordingto the invention, the rectifier for the anode circuit of tube I consists of a grid controlled rectifying tube III, suitably a gas-filled thyratron tube, the anode of which is connected to one of the terminals of the transformer winding SI, and the heating current of which is supplied from the winding St on the transformer T. Such a tube has the characteristic, that at-a certain negative grid voltage it works as a normal rectifier. If, on the other hand, the negative grid voltage increases up to a certain value, the tube ceases to glow. In the circuit shown in' Fig. 2, the extinction of tube III entails that the anode voltage for tube I ceases. Tube II thus ceases to function and relay A breaks the current supply to the heating element E. If tube III can thus be extinguished when the transmitter R6 becomes short-circuited, safety is obtained in that the oven element E will be turned off upon suchg short-circuit, and the condition for this will thus be, that the negative grid voltage of tube III becomes sufiiciently high upon occurrence of a short-circuit in the transmitter. This can be accomplished by supplying said grid from a winding S4 on transformer T with a voltage which, by means of the potentiometer R1, is set to such a value that the grid, merely because of said voltage, receives a negative voltage having such a magnitude that thetu'be III'is blocked during that half cycle in which the anode is positive. The voltage drop across the resistance R6 is therefore applied over the line L2 and the transformer T! to the grid of tube III. The grid voltage on tube III is thus determined by the voltagesfromlfl and S4 and the circuit is arranged so that the voltage from Ti and the blocking voltage from S4 are out of phase by an angle on account of which the blocking voltage from S4 is counteracted by the voltage originated at R6. The magnitudes of said two voltages are chosen so that their resultant in normal cases has such a value that. during the half cycle when the anode is positivathe tube is not blocked, due to which tube III thus as in normal cases operates as a rectifier. If the voltage drop'across transmitter RE new disappears due to the transmitter being short-circuited, the voltage on the grid in tube III will be determined exclusively by the voltage from winding S 3, and tube III thereby, as-mentionedabove, will be blocked, which ensures that the anode circuit of tube I is broken, relay A thereby breaking the current supply to the oven heating element E over contact It.

By means of a-regulator of the type just described, the oven temperature is thus prevented from. exceeding the predetermined value even if the transmitter or its leads becomes inoperative from either short-circuit or open circuit conditions. 1 I

The invention can be modified in several difierent wayswithinthe scope of the invention. For example, if the circuit comprises only one elec- N tron-tube, therelay Winding A and the rectifier tube III will be connected in series in the anode circuit of said tube.

1 1'. A regulating device for automatically maintaining the condition of a quantity at a predetermined value, comprising a resistance bridge, one armiof said bridge including a resistor whose resistance varies :in accordance with the condition of saiduquantity, a source of alternating current connected-across opposite input terminals of said bridge, a, first and a second space discharge'device each comprising at least an anode, a cathode and a control grid, said devices being connected in cascade with the cathode and control grid of the first device connected across opposite ,output' terminals of said bridge, a relay comprising an operating coil and contacts controlled thereby, a" circuit connecting said coil, said source and the anode-cathode path of the second device all in series'relationship, means controlled by the condition of said contacts for varying'the condition of said quantity, a gridcontrolled rectifier tube energized from said source and connected to supply anode voltage to said first device, means for applying an alternating bias voltage from said source to the grid of said-rectifier tube/a shunt circuit across said resistor for deriving an alternating voltage from current passing'therethrough, and means i or applying'saidalternating voltage to the grid of said rectifier tube in phaseopposition to said bias voltage, said voltages being so adjusted that their conjoint effect upon said rectifier is insufiicient to block conduction of the same until the voltage developed across said'resistor drops below a pre determined minimum corresponding to a short circuit thereof.

2. The invention in accordance with claim 1, in which said rectifier includes a cathode, a circuit for deriving cathode-heating current from 3. The invention in accordance with claim 1, 5

in which said resistor comprises thermally responsive material, and in which the means for varying the condition of said quantity comprises a heating element.

4. The invention in accordance with claim 1, in which said rectifier tube comprises a gasfilled thyratron tube.

SETH AUGUST I-IOLMQVIST.

6 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,011,970 Dawson Aug. 20, 1935 2,102,664 Alexander Dec. 21, 1937 

